1. Field of the Invention
The present invention relates to a method and apparatus for opening and closing lateral boreholes and particularly, but not exclusively, to a method and apparatus for selectively opening and sealingly closing a lateral borehole.
2. The Prior Art
It is well known in the oil and gas drilling industries to provide a primary borehole with one or more lateral boreholes. The deflection of downhole equipment from the primary borehole into a lateral borehole may be readily achieved through location of a deflector/whipstock downhole of the primary/lateral borehole junction. It is also known for the types of deflector/whipstock used in this manner to be provided with an axially extending bore for allowing access to the portion of primary borehole located downhole of said junction. In this way, use of the primary borehole or an associated lateral borehole may be selected. However, if use of the lateral borehole is no longer required or not required for considerably long periods of time, then it can be desirable to close the opening in the primary borehole which extends into the lateral borehole. However, closing the opening in the primary borehole requires removal of the deflector so that specialist closing equipment can be employed. This is time consuming, costly and inconvenient.
It is an object of the present invention to provide a method and apparatus for controlling access to a lateral borehole.